This invention relates to a process for production of a bleaching clay product from naturally acidic hormite clay by adding extremely small quantities of acid to the mined and crushed hormite clay. In addition, this invention relates to a process for the production of a bleaching clay product by aging the crushed, naturally acidic hormite clay for an extended period of time, and more particularly, by adding extremely small quantities of acid to the aged hormite clay product. In addition, the invention relates to products produced by these processes.
It is well known that many naturally occurring clays may be used to decolorize oils. These clays decolorize or bleach various oils, such as mineral oils and vegetable oils; various fractions from petroleum, especially lubricating oils, and can be used for refining used lubricating oils, as well as purifying animal fats and beeswax.
In the early 1900""s, it was discovered that the bleaching power of naturally-occurring clays could be enhanced by treating those clays with relatively large quantities of a mineral acid, such as hydrochloric or sulphuric acid, and then washing the acid treated clay free of dissolved salts and residual acid created by the acid treatment. This process is conventionally called acid activation. The general process of acid activation of a clay product includes grinding the clay to a generally uniform size, dispersing the clay in water, slurrying the ground clay, and then adding the acid to the clay slurry to form substantially uniform, acid-activated bleaching clay products. This process is disclosed, for example, U.S. Pat. Nos. 1,492,184; 1,781,265; 2,018,987; and 2,671,058.
While many processes are useful for acid activation of various types of clay products, the oils being treated with the acid-activated clay can be damaged by the acid utilized with these processes. Because of this adverse effect, it is conventional practice to wash the clay after acid activation to remove any excess acid. However, that washing creates a waste stream that can contain minerals and acids that are harmful to the environment, and which must be neutralized or otherwise disposed of in an environmentally reasonable manner.
U.S. Pat. No. 5,008,226 has addressed this issue by limiting the amount of acid that is utilized for activation. Thus, after acid activation, it is claimed that this bleaching clay product need not be washed. This patent teaches the addition of from 1 to 10 percent by weight of concentrated sulfuric acid to certain naturally-occurring mixtures of palygorskite and bentonite clays. The preferred range of acid addition is between 3 and 5 percent. Even though the level of acid used in the activation of this clay is low in this process, the acid is still expensive and the bleaching clay product produced can still not be used for the bleaching of certain types of edible oils because of the presence of the acid.
A process for producing an acid-activated, decolorizing clay using a naturally occurring, acidic attapulgite clay with a pH in the range of 5 to 7 and a pore volume in the range of 0.25 to 0.50 cm3/g is known from U.S. Pat. No. 5,008,226. This clay is activated by the addition at a temperature of 25 to 100xc2x0 C. (77 to 220xc2x0 F.) of an acidic solution equivalent to 10 percent to 30 percent of the clay by weight. This acid-activated clay is not washed, but is used directly as a decolorizing clay.
Aside from attapulgite clay, bentonite clays can also be activated with acid, but higher concentrations of acid are recommended than for attapulgite clay. Because of the relatively large amounts of acid used during this acid activation, release of acid by the decolorizing clay to the material being decolorized cannot always be avoided.
A process for acid treatment of an attapulgite clay to produce an improved cat litter is known from U.S. Pat. No. 3,029,783. Relatively low percentages of acid are used in this process, and the acid-treated material is not washed. The material is calcined at 370 to 540xc2x0 C. (700 to 1000xc2x0 F.) before the acid treatment, with another calcination at about 400 to 590xc2x0 C. (750 to 1100xc2x0 F.) occurring after the acid treatment. These treatments are necessary to increase the ability of the attapulgite to absorb urine and other body fluids. Use as a decolorizing clay is not discussed.
U.S. Pat. No. 1,492,184 describes a process for the activation of crude clay with acid, wherein the acid constitutes not more than 10 percent by weight of the clay. Calcining is expressly avoided to prevent evaporation of the acid.
A process for acid activating a clay is also disclosed by U.S. Pat. No. 4,847,226. In this process, the clay is extruded and ground, and an aqueous acidic solution is added to produce a suspension. The suspension is heated, and the acid-treated clay is separated, washed, filtered and dried. There is no heat treatment of the acid-activated clay. The intent of this treatment is to improve the ability of the clay to filter impurities from liquids. In particular, oil-soluble dyes are said to be removed from oils using this product.
Numerous patents have disclosed acid treatment of various types of absorbent clays. In these patents, the amount of acid that is utilized varies considerably, based on the type of clay utilized and whether the clay is washed after the acid activation step. However, in most circumstances the amount of concentrated acid added exceeds ten percent (10%) by weight. These patents include: U.S. Pat. Nos. 1,844,476; 1,792,625; 1,796,799; 3,617,215; 1,752,721; 1,716,828; 1,455,995; 1,949,673; 2,602,807; 1,544,210; 2,981,697; 1,946,124; and 2,484,828.
Processes for the regeneration of spent acid-activated bentonite clay are disclosed in U.S. Pat. Nos. 5,468,701 and 5,330,946. See also U.S. Pat. Nos. 2,477,386 and 2,671,058.
It has now been discovered that even the relatively low percentages of acid taught by some of the prior art patents may have an adverse effect on the bleaching clay product and/or on the oil being bleached by the bleaching clay product.
Accordingly, it is an object of this invention to disclose a process for the production of a bleaching clay product, whereby extremely small amounts of acid are added to the preliminary clay products.
It is a still further object of this invention to disclose a process for the production of a bleaching clay product which can be effective for the bleaching of certain types of oil, even with no acid activation.
It is a still further object of this invention to disclose a process for the production of a bleaching clay product which can be activated by merely aging the clay product in situ for an extended period of time without adding any acid to the clay product.
It is a still further object of the invention to disclose bleaching clay products produced by the process of adding acid at levels less than 1 percent by weight to a crushed hormite clay that has been aged for an extended period of time.
These and further aspects of the invention will be apparent from the foregoing description of the preferred embodiment of the process and the product produced by that process.
One preferred process for the production of a bleaching clay product of this invention comprises selecting a naturally occurring, raw hormite clay product, cleaning the raw hormite clay product, crushing the cleaned, hormite clay product to produce hormite clay clumps, wherein preferably at least about fifty percent (50%) by weight of the clumps are less than about 6 ins. in diameter, aging the hormite clay clumps for a period of time, preferably at least three (3) months in situ, drying the aged hormite clay clumps, and milling the dried hormite clay to form a bleaching clay product with a residual acidity of less than about 0.25 percent by weight, preferably less than 0.2 percent by weight and most preferably less than 0.15 percent by weight.
An additional preferred process for the production of a bleaching clay product comprises selecting a naturally occurring, raw hormite clay product, cleaning the raw hormite clay product, crushing the cleaned hormite clay product to produce hormite clay clumps, wherein preferably at least about fifty percent (50%) by weight of the clumps are less than about 6 ins. in diameter, and treating the hormite clay clumps with less than 1 percent by weight, based on the dry weight of the clay product, of a concentrated acid. Preferably the amount of acid added is less than 0.5 percent, and most preferably from about 0.3 to about 0.5 percent. The acid treated hormite clay clumps are then dried and milled to form a bleaching clay product with a residual acidity of less than about 1 percent by weight, preferably less than 0.5 percent by weight. No washing of the bleaching clay product is necessary.
An additional preferred process for the production of a bleaching clay product comprises selecting a naturally occurring, raw hormite clay product, cleaning the raw hormite clay product, crushing the cleaned, hormite clay product to produce hormite clay clumps, wherein preferably at least about fifty percent (50%) by weight, of the clumps are less than about 6 ins. in diameter, aging the hormite clay clumps for an extended period of time, preferably at least about 3 months, and treating the hormite clay clumps with less than 1 percent by weight, based on the dry weight of the clay product, of a concentrated acid. Preferably the amount of acid added is less than 0.5 percent by weight, and most preferably from about 0.3 to about 0.5 percent, by weight. The acid treated hormite clay clumps are then dried and milled to form a bleaching clay product with a natural acidity of less than about 0.5 percent by weight.
In addition, the invention includes products produced by these processes for the production of bleaching clay products.